Again, operational definitions of defects and categories are vital. In many cases, the number of defects observed will increase with the time available for inspection. A good operational definition, specifies the time to be allocated to inspecting each item. Attributes are particularly vulnerable to variable interpretations where there are no operational definitions. A specification demands "no visible defects." How do you pass all the parts? Turn out the lights!
Visual aids should aid inspectors in deciding marginal cases rather than describe the obvious. They should be displayed in the inspection area and photographed under representative lighting conditions. There is little excuse for not using colour these days though issues of colour matching should be treated with care. Don't forget that your inspectors may suffer from colour-vision deficiencies. A good example, illustrating a well-defined Likert scale, is the Beaufort scale for wind speeds.
This page last updated 13th July 2001
Copyright ©2001 A N Cutler